Multicast is the simultaneous delivery of information to a set of network destinations that form a multicast group. By comparison with multicast, conventional point-to-single-point delivery is called unicast, whereas delivery to every node of the network is broadcast.
Modern cellular networks provide the capability to support multicast services such as voice conferences and video conferences. In general, a particular multicast service may very efficiently serve the members of a multicast group over a single channel if the members are all located in a single cell. However, In many cases it is not possible or not feasible to locate all members in a single cell. Moreover, in cellular networks (and in particular in networks having a hierarchical cell structure, also called multitier cellular networks) a member of a multicast group may often belong to one of several spatially overlapping and/or hierarchically related cells. In such situations, techniques are useful for assigning the multicast group members such that the network capacity is increased (e.g., in terms of the number of multicast groups that can be served by the network).
Assignment techniques for spatially overlapping or spatially adjacent cells are often defined in so called hand-over schemes. Such hand-over schemes are specifically tailored for unicast services and are therefore not (or not readily) applicable to multicast services.
One exemplary assignment technique for networks having a hierarchical cell structure is described in Il Han et al. “An Efficient Channel Allocation Scheme for Multicast Traffic in Multitier Cellular Systems”, IEICE Transactions on Communications, April 2001, E84-B(4), 1087-93. The technique proposed by Il Han et al. relates to a two layer hierarchy with microcells and macrocells, each macrocell including a plurality of microcells. A term “microcell group size” is introduced that specifies the number of microcells in which members belonging to a particular multicast group exist. Assuming that the members of the multicast group that are located in a single microcell are served via a single channel, the number of channels needed for serving the multicast group equals the microcell group size. If all members of the multicast group were located in a macrocell, only a single channel would be needed. However, if only macrocells provide the multicast service, significant capacity decreases may occur.
According to the technique proposed by Il Han et al., all members of a multicast group are assigned to either a macrocell or a microcell depending on the microcell group size. The group members are all assigned to a macrocell if the microcell group size would exceed a predefined threshold parameter. Otherwise, microcell channels are allocated to all group members. Although this decision mechanism can be implemented quite easily, setting of the threshold parameter is a difficult task in scenarios with varying network traffic.
It will be appreciated that there remains a need for flexibly assigning multicast group members to radio network cells such that network capacity is increased.